1. Technical Field
The following description relates to one or more image readers configured to read an image of a document sheet, particularly to one or more image readers each of which supplies a predetermined driving current to a plurality of light sources emitting respective different-color light beams to read the image of the document sheet.
2. Related Art
So far, an image reader has been proposed, which includes a reading unit configured to read a document sheet while moving relative to an image on the document sheet. The reading unit includes a plurality of light sources that emit respective different-color light beams, a light introducing portion that introduces the light beams emitted by the light sources onto the document sheet, and a light-receiving portion that has light-receiving elements arranged linearly along a main scanning direction and outputs a reading signal corresponding to a light intensity of a light beam which is reflected from the document sheet and received by each light-receiving element.
In the above-configured image reader, it is possible to detect a distribution of an intended color in the main scanning direction on the document sheet by causing one of three light sources emitting light beams with respective different colors, red (R), green (G), and blue (B) to emit the intended-color light beam and determining the light intensity of the light beam received by each light-receiving element. When performing such a process with respect to each of the three colors while the reading unit, which includes the light sources, the light directing portion, and the light-receiving portion, moves relative the image on the document sheet, the image reader reads the whole image on the document sheet as a color image. In addition, an image reader has been proposed that is configured to read the image on the document sheet as a monochrome image by causing the light sources to sequentially emit the different-color light beams and determining the summation of the light intensities of the different-color light beams received by each light-receiving element.
Further, when employing a circuit configured to supply the same level of driving current to each light source, the image reader has only to include a single unit for adjusting the driving current. Thus, it is possible to provide the image reader with a simplified configuration. However, in such a case, since the respective light intensities of the different-color light beams emitted by the light sources are different from each other, respective light-emitting times during which the light sources emit the light beams in a predetermined reading period of time have to be separately set. Thus, when a light-emitting time is set separately for each of the light sources, it is impossible for all the light sources to emit the light beams over the entire reading period of time. Namely, it might result in a situation where the reading period of time includes a non-light-emitting time during which none of the light sources emits a light beam. Thus, an image reader has been proposed, which is configured to, when reading the image on the document sheet as a color image, set side-by-side respective light-emitting moments at which the light sources emit the light beams, so as to restrain “color shift.”